432 PROTEINS 



value in distinguishing the various compounds from each other. 

 Following upon the researches of Wassermann and Uhlenhuth, 

 Tstistowitch found that serum drawn from a rabbit, which had 

 been inoculated for some time with the serum of a horse, had 

 acquired the property of producing a precipitate when added 

 to normal horse serum ; this is due to the formation in the 

 rabbit's blood of a substance known as a precipitin, which 

 belongs to a class of compounds described by Hofmeister as 

 pseudo-globulins ; the precipitate formed is a compound of 

 the precipitin with the albumin contained in the serum to which 

 the precipitin was added. The precipitin so prepared should 

 only react with horse serum and not with the serum of any 

 other animal ; the reaction is, however, not absolutely specific, 

 inasmuch as a precipitin may react with the serum of an 

 animal closely related to the one from whose serum it was pre- 

 pared. It has, moreover, been found that substances which 

 had been isolated from natural fluids, as well as native sera, 

 were able to incite a precipitin formation when injected into 

 the blood of some living animal, and it has been thus possible 

 to show that the albumin contained in milk is not identical 

 with that obtained from blood. The method has been em- 

 ployed by Kowarski and Schiitze * for distinguishing the vari- 

 ous plant albumins, and by Rickmann,t Uhlenhuth, J and 

 others for distinguishing between horse flesh and the meat of 

 other animals. An attempt has also been made to employ 

 the same principle for the estimation of proteins by a com- 

 parison of the precipitates formed under various conditions. § 

 As illustrating the very close connection existing between 

 albumins and globulins, it is worthy of note that Moll claims to 

 have converted serum albumin into serum globulin by warming 

 a 3 per cent solution of serum albumin for one hour to 60° C. 

 with N/66 sodium carbonate, but it is difficult to say whether 

 true serum globulin was actually produced. According to 



* Kowarski and Schiitze : " Deut. med. Wochenschr.," 1901, 27, 442 ; 

 1902, 28, 804. 



t Rickmann : " Chem. Zeit.," 1907, 2, 1983. 



X Uhlenhuth and Weidanz : " Praktische Anleitung z. Ausfiihrung des 

 biolog. Eiweissdifferenzierungsverfahren," Jena, 1909. 



§ Schulz : "Deut. med. Wochenschr.," 1906. 32, no. 26; "Zeit. 

 Unters. Nahr. u. Genussm.," 1906. 12, 257. 



